Froth flotation of cryolite



United States Patent 3,082,872 FROTH FLOTATION F CRYOLITE Artur ErnstHeinrich Bergmann, Meggen A.D. Lenne, Germany, assignor toKlockner-Humholdt-Deutz Aktiengesellschaft, Koln-Deutz, Germany, acorporation of Germany No Drawing. Filed May 3, 1961, Ser. No. 107,327Claims priority, appiication Germany May 6, 1960 4 Claims. (Cl. 209-167)My invention relates to a froth flotation method for cryolite.

Cryolite deposits generally contain about 80 to 85% cryolite, theremainder being fluorspar, iron spar (siderite), quartz, sulfides,thomsenolite, pachnolite and hagemannite.

It is an object of my invention to eliminate the just mentionedimpurities by a froth flotation method.

Since the ore is often intimately mixed with gangue, the ore must beground down to minus 100 microns (0.1 millimeter).

According to a known method, the ore is first subjected to sulfideflotation, whereafter the cryolite itself is activated by addition ofsodium fluoride, so that it can be carried off by means of fatty acidsor their soaps, after several subsequent purifying stages. This methodhas the following disadvantages:

(1) Several subsequent purifying stages are necessary (2) A longfroth-forming time and therefore a large cell volume is necessary,because the major portion of the ore, cryolite, is floated away;

(3) Cryolite, enriched in the froth, causes considerable difliculties inthe further fabricating processes because such cryolite is no longerwettable.

According to my invention, a considerable improvement of the flotationprocess is achieved by proceeding as follows. The pulp, in acidiccondition, is provided with copper sulfate or a similar medium and isprocessed by means of a collecting agent and a frothing agent, in orderto float away the major portion of the impurities. The first stagedischarge is then floated in a second stage by use of afatty-alcohol-phosphorus acid ester salt, likewise in an acidic bath, inorder to float away the residue of the impurities. The flotation iseliected in an acidic pulp in order to prevent floating of the cryolite.

In the first stage, the sulfides of the gangue are sufficientlyactivated by the addition of copper sulfate and an acid. Conversely, thecryolite is sufliciently passivated by addition of the copper sulfate.When quartz is present in the gangue, the method of the invention can befurther improved by adding a cation-active medium, for example an amine,to the second stage. This has the advantage of increasing theelimination of quartz.

The following example relates to an ore containing on the average 80%cryolite, 3% fluorspar, 8% siderite, the residue consisting of quartz,sulfides, pachnolite, thomsenolite and hagemannite. The ore was groundto a grain size of minus 100p and was processed in the first flotationstage at 250 g. solids per liter. Sulfuric acid was used to adjust thepH of the pulp to about 5.0. City water of Cologne, Germany, having ahardness of 17 DH was the water used. The reagents used were as follows:

Stage 1 1O kg./t. CuSO 300 g./t. H 50 200 g./t. potassium ethyl xanthate(collecting agent) 40 g./ t. pine oil (frothing agent) The first stageconcentrate was supplied to a second flotation stage in which thefollowing reagents were consumed:

Stage 2 250 g./ t. sodium laurylphosphate 55 g./t.laurylpyridiniumbromide (cationic collecting agent) It is preferablethat the sodium lauryl phosphate is added to the second stage in twoportions, of which the second portion is added toward the end of thesecond flotation stage. It is also preferable to add the cationiccollecting agent at this time. As a rule, it is not necessary to addacid in the second stage, because the addition of acid to the firststage is suflicient in most cases for the second stage also to beacidic. In the example described above, the pH value in the second stageincreased to about 6.8.

The flotation had the following result:

Cryolite Weight Percent Percent Percent Output Froth products 30. 6 36.00 14. 0 Concentrate 69. 4 97. 08 86. 0

In another example, the following reagents were consumed:

Stage 1 10 kg./t. CuSO 200 t. H2804 200 g./t. potassium ethyl xanthate(collecting agent) 40 g./t. pine oil (frothing agent) Stage 2 250 g./t.sodium laurylphosphate 55 g./t. laurylpyridiniumbromide The pH valueswere similar to those listed in the first example.

The flotation had the following result:

1. A froth flotation method for recovering cryolite, comprisingacidifying a cryolite ore pulp, said cryolite ore pulp containingimpurities comprising sulfides, fluorspar and siderite, adding in afirst stage copper sulfate, potassium ethyl xanthate and pine oil tofloat the sulfide impurities, adding in a second stage sodiumlaurylphosphate to float the remainder of the impurities.

2. A froth flotation method for recovering cryolite, comprisingacidifying a cryolite ore pulp, said cryolite ore pulp containingimpurities comprising sulfides, fluorspar, siderite and quartz, addingin a first stage copper sulfate, potassium ethyl xanthate and pine oilto float the sulfide impurities, adding in a second stage sodiumlaurylphosphate and laurylpyridiniumbromide to float the remainder ofthe impurities.

3. A froth flotation method for recovering cryolite, comprisingacidifying a cryolite pulp containing impurities comprising sulfides,fluorspar and siderite to a pH of 5, adding in a first stage coppersulfate, potassium ethyl xanthate and pine oil to float the sulfideimpurities, adding in a second stage sodium laurylphosphate to float theremainder of the impurities.

4. A froth flotation method for recovering cryolite, comprisingacidifying a cryolite pulp containing impurities comprising sulfides,fluorspar, siderite and quartz to 5 a pH of '5, adding in a first stagecopper sulfate, potassium ethyl xanthate and pine oil to float thesulfide impurities, adding in a second stage sodium laurylphosphate andlaurylpyridiniumbromide to float the remainder of the impurities,whereby the major portion of the cryolite 10 remains in the concentrate,

References Cited in the file of this patent UNITED STATES PATENTSSchranz July 17, 1934 Lenher Oct. 11, 1938 Zenftman Aug. 21, 1956Goldenhar Dec. 20, 1960 Hazen June 5, 1962 FOREIGN PATENTS Germany Aug.27, 1937

1. A FROTH FLOTATION METHOD FOR RECOVERING CRYOLITE, COMPRISINGACIDIFYING A CRYOLITE ORE PULP, SAID CRYOLITE ORE PULP CONTAININGIMPURITIES COMPRISING SULFIDES, FLUORSPAR AND SIDERITE, ADDING IN AFIRST STAGE COPPER SULFATE, POTASSIUM ETHYL XANTHATE AND PINE OIL TOFLOAT THE SULFIDE IMPURITIES, ADDING IN A SECOND STAGE SODIUMLAURYLPHOSPHATE TO FLOAT THE REMAINDER OF THE IMPURITIES.